Currently, various kinds of navigation apparatuses that are attached to movable bodies, such as automobiles, and detect a position, a traveling speed, and a traveling direction of the movable body and displaying information for assisting in traveling toward a destination have been devised. With such navigation apparatuses, a position of the device itself is detected based on positioning signals from positioning satellites, such as GPS satellites, and a moving state of a movable body is detected by using speed information that the movable body already has, such as a vehicle speed pulse in an automobile, and azimuth information that is obtained by, for example, a gyroscope.
Meanwhile, recently, as alternatives to the navigation apparatuses described above that are installed in the movable bodies in advance and can acquire, for example, the speed information of the movable body, various personal navigation devices that can perform a navigation as a stand-alone navigation devices by, for example, acquiring speed information, and are comparatively compact sized and portable have been devised. Therefore, by attaching such a personal navigation apparatus to a movable body, even if a navigation apparatus is not installed in the movable body in the first place, a navigation system can be used.
When using such personal navigation apparatuses, depending on an attached angle on the movable body, that is an attached angle of an accelerometer within the personal navigation apparatus on the movable body, there is a case where a traveling speed and a traveling azimuth of the movable body cannot correctly be obtained and a navigation cannot correctly be performed. Therefore, an attached angle calculating device such as the one disclosed in either one of Patent Documents 1 and 2 is installed in the navigation apparatus, the attached angle of the accelerometer is calculated, and an acceleration is corrected.